If a terrorist told a pilot he had a bomb on board, the pilot would likely NOT take the plane over a populated area, PARTICULARLY in light of 9/11/01. Personally, a terrorist would have to kill me and take over the controls himself to get it over a populated area. I suspect most pilots would feel the same way. Oftentimes, when you hear about a plane crash that could have killed more people on the ground, the pilot did his/her best to get it away from populated areas.
Which could explain why the plane took an abrupt turn.